1. Field of the Invention
The present invention relates to signal filter means for use between a cable and a high frequency electric connector and more particularly, to a signal filter assembly, which uses filters each formed of a parallel circuit of one resistor and one capacitor to automatically adjust the impedance between the cable and the high frequency electric connector, and which attenuates the voltage level to keep the high frequency level and the low frequency level equal.
2. Description of the Related Art
There is a great change in audio and video applications in recent years, and many high-tech video apparatus and systems such as disc player, high-resolution digital TV, videophone, video conference system, and etc., have entered outer life. Comparing to conventional techniques, these high-tech video apparatus and system process video signal in a digital form. Following the demand for application in different fields, related standards have been established and modified to a perfect state. In order to let users enjoy better quality, suppliers are trying hard to increase the bandwidth of digital signal so as to provide better picture quality and sound quality.
However, following the increase of system working frequency and the miniaturization of electronic devices, related electric connectors are made relatively smaller. In consequence, a greater level of high frequency noise is produced due to non-match of impedance. Various factors including line width, material thickness, copper foil thickness, material's coefficient of dielectric constant, solder mask, etch factor, and etc. cause the occurrence of noise. Crosstalk is the most common problem. Crosstalk is produced upon interference of the magnetic waves from a dynamic signal with the neighbor signal line. This problem becomes more serious during the transmission of a high frequency. The crosstalk between two signals is subject to the relative capacitance value and inductance value. Normally, the crosstalk caused by the inductance is more serious than the crosstalk caused by the inductance in digitalization. A crosstalk will cause the following effects.
a. Variation of equivalent characteristic impedance.
b. Variation of transmission speed.
c. Incomplete of signal.
d. Lowering of noise margin.
Further, the cable is also an important factor that affects the crosstalk. In order to transmit a signal to a farther place, the length of the cable must be relatively increased. However, extending the length of the cable will relatively increase the crosstalk. When using a better cable in order to reduce the crosstalk, the installation cost is relatively increased.
Further, in early days, CRT monitors were commonly used in TV and computer systems for the advantages of good quality and low price. Nowadays, various planar displays including TFT LCD and PDP have been developed and have appeared on the market. These planar displays are developed to provide a better picture quality. In order to obtain a better picture quality, digitalization is employed to process image noises. For a better picture quality, a broad bandwidth is required. In consequence, the crosstalk will be relatively increased. If a transmission line is used to transmit a high frequency signal to an electronic product (TV, LCD) directly without considering the problem of crosstalk, the crosstalk will affect the quality of the picture, resulting in edge blur and unclearness of layering. Thus, it is not possible to obtain a better picture quality.